非球面补偿板三维面形检测方法的研究

本文对准直激光束检测非球面方法进行了研究。它不用接触被检件表面,同时也无须处理干涉条纹。测量时只要保证激光细束保持一致的入射方向扫描被检表面,用CCD光电探测器检出面形的斜率变化,而后在扫描范围内积分便能获得面形高度。本文以测量光学系统中用于波面补偿目的的旋转对称镜面为例对测量系统进行分析。该系统不仅可以进行一维测量,通过转台旋转亦可进行二维测量,通过面形重构获得三维的被测体面形。给出了三维面形重构方法,并编制数据处理软件,可以把测量数据处理成高度曲线或三维面形。     

新型自由曲面三维激光扫描系统

从机械结构、控制系统及操作系统结构等几个角度介绍一种三维激光扫描系统设计方案。系统集成了先进的数据处理技术、激光扫描技术、先进控制技术及机器人技术,有效地借助于光机电一体化技术实现了表面检测及三维表面模型重构智能化及自动化。系统由具有电驱动装置的激光测头、C形滑臂、升降旋转台、电控系统及主控计算机组成。通过所设置测量参数,系统能够对不同的被测物体进行扫描路径规划,进而通过激光测头、C形滑臂及转台的全自动协调控制完成无盲点三维表面测量任务。试验结果表明,该三维激光扫描系统的扫描精度达到0.1 mm,速度为10 000点/s,能够应用于小型工件及模型、模具表面数据检测及模型重构。     

高陡度保形光学镜面的坐标测量

针对高陡度保形光学镜面的检测,提出了基于多段拼接的光学镜面坐标测量方法。该方法将保形光学镜面轮廓的测量分割为具有一定重叠区域的数段较短的面形轮廓的测量,通过测量系统与被测工件之间的相对旋转与平移运动调整被测工件的姿态实现分段轮廓的测量。然后使用拼接算法将各段面形轮廓拼接起来,重构出被测工件的面形误差。建立了该坐标测量法的数学模型,提出了基于最小二乘的迭代拼接算法,并在Matlab下对测量算法进行了仿真。开发了高精度的测量试验系统并分别在VC与Matlab下编写了测控软件与数据分析软件。对一口径为120mm,长径比为1.2的椭球形保形头罩进行了实测试验。仿真与测量试验表明,上述方法能够高精度地重构出面形轮廓,方法简单,实用。     

平面式大型微结构表面的螺旋扫描测量

为实现平面式大型微结构表面的快速测量,提出了一种螺旋式扫描测量方法。基于该方法的测量系统由x、y、z向直线运动平台、绕z轴旋转的直接驱动(DD)马达以及激光位移传感器组成,当移动x、y向平台使激光位移传感器的激光束与DD马达的旋转中心重合,并通过z向平台使激光位移传感器位于其测量范围内时,使x向平台与DD马达同步运动而形成螺旋线来获得被测表面形貌的平面位置信息,同时由激光位移传感器获得被测表面的高度信息,据此实现对被测表面形貌的测量;这种螺旋式扫描方法避免了栅格式扫描方法所存在的频繁加减速及反向运动间隙不足的问题,可提高系统的测量速度和精度。基于所搭建的测量系统,对表面形貌为凸凹扇形的圆形试件的表面进行了测量,结果表明:所提出的螺旋式扫描方法能够实现表面三维形貌的快速测量,测量试件表面上直径为Φ20 mm的区域时,所用时间仅为800 s,测量结果能较好地反映被测试件表面形貌的三维形貌。     

提高自由曲面透镜测量精度的迭代重构曲面算法研究

在提出的基于图像变换的光学透镜的表面面形测量方法中，建立了造代重构曲面算法。算法根据待测透镜光学表面在光学成像系统中的图像变换特性，重构出与待测透镜光学表面具有相同图像变换特性的数值三维曲面簇，利用造代方法从中筛选出与待测透镜光学表面面形完全相同的数值三维曲面，解决了测量精度不足的问题。实验结果表明，使用该算法所构建的数值曲面与待测透镜光学表面的曲面面形能够准确相符。     

基于薄片测头的外形几何测量及其数据还原方法

提出应用薄片圆盘滚动接触头,采用扫描测量的方法测量复杂表面几何形体.减小因接触头厚度导致接触点变化而产生的误差,可以实现对空间三维曲面体进行连续测量,提高表面测量的精度和速度.通过对薄片圆盘滚动接触头的中心轨迹求得法线方向,并沿着法线内移一个薄片圆盘滚动接触头半径距离的点即为接触头与被测表面的实际接触点.根据接触点得到被测表面实际几何点云数据,进行三维造型的重构或进行三维图形的显示等工作.以鞋楦的测量为例加以说明,并制造了用于鞋楦外形的测量设备,取得了满意的结果.     

复杂轮廓表面的线式扫描单目成像测量方法

采用单摄像机和线式激光源,通过使被测物体连续旋转,实现了对复杂轮廓表面的三维非接触测量,并详细说明了数据处理过程.该方法可使测量效率显著提高,测量精度主要取决于被测物体的旋转控制精度和摄像机的分辨率.     

基于主成分分析的大型管道三维表面重建

针对大量的点云数据要求快速、方便且精度高的特点,在轮廓线拼接建模方法的基础上提出一种结合主成分分析的三维表面建模方法。由结构光扫描系统获得点云;通过热传导模型将点云进行片层分割并进行主成分分析,得到纬度圈,从而获得纬度圈上的所有对应点对;在相邻点对之间进行柱面插值连接,生成物体的四边形网格模型和三维表面模型。结果显示,被测管道重构表面平均误差为0.19 mm,小于采用基于轮廓线拼接方法得到模型的平均误差。结果表明,采用基于主成分分析的方法进行管道三维表面重构,其精度得到了有效地提高,满足工程测量的精度要求;同时也证明了该方法的正确性。该重构方法适用于表面是一阶连续性被测物体尺寸及变形的分析。     

基于调制度的光学三维测量的研究

为了能够测量复杂的面形物体,在基于调制度的光学三维测量研究中,提出利用改变光栅投影系统的物距,实现光栅图像对物体的纵向扫描,从而获取所测物体表面各点调制度的极大值,恢复物体的高度信息。运用此方法便于实现三维测量仪器的小型化,减少误差,可避免在相位测量中需要去包裹的问题。     

大型管道快速测量与建模技术研究及应用

为了提高大尺寸管道测量效率和测量精度,搭建了一套具有快速、高精度、密集点云采集、实时数据处理等功能的扫描测量系统。基于坐标系变换理论,提出了一种数字摄影测量技术、双目结构光扫描技术和逆向工程重构建模技术的组合式测量方案,快速便捷地获得大范围高密度的物体表面点云,并利用三维重构软件对物体表面测量数据进行曲面重构,利用误差合成理论对测量及曲面重构过程中的误差进行了分析,论证了该方法在理论精度上满足工业生产对逆向工程的要求。将该组合式测量系统应用于大型锻造管道的测量重构,在效率和精度等各方面都取得了良好的效果。     

Wolter I型反射镜面形在线检测装置设计

由于传统的基于干涉原理的测量方法无法对用于太阳X射线成像仪的Wolter I型旋转非球面反射镜进行检测,本文提出了一种在线检测此类反射镜面形的方法。以长程轮廓测量仪的原理为基础,经过改进、整合测量装置并在扫描机构中加入五角棱镜转折光路,搭建了一套Wolter I型旋转非球面反射镜面形检测装置,并对该装置的工作原理、结构参数设定以及数据处理算法等进行了研究。用一块标准平面反射镜作为基准面对该装置定标,并通过实测反射镜样品进行验证实验。实验结果表明:该装置的倾斜度测量误差为RMS 6.7 μrad,重复精度为0.75 μrad,轮廓测量精度约为PV 0.24λ,RMS 0.07λ,基本满足设计要求。     

Calibration for the sensitivity of multi-beam angle sensor using cylindrical plano-convex lens

A highly sensitive and compact multi-beam angle sensor (MBAS), which utilizes the principle of operation of an autocollimator, was developed to detect the differential of the local slope components (angle difference) of a point on the mirror surface and using Fourier series, we can obtain the profile data from the angle difference. In order to investigate the application of the MBAS for high precision aspheric surface measurements, two types of calibration methods using plane mirror and cylindrical plano-convex lens has been proposed to measure the sensitivity of the MBAS. The calibration data analysis results using plane mirror agree well with the measurement results of the cylindrical plano-convex lens data. Comparison of the two methods confirms that the second method (using cylindrical plano-convex lens) is more adapted for measurement with ultra high level of uncertainty. Further, the second method is simple, corresponding to a direct calculate in the sensitive parameters aiming to minimize the cost.     

用干涉条纹图像重建反射镜的三维面形

给出了用干涉条纹图像重建反射镜三维面形的方法,用泰曼-格林干涉仪采集被测镜面的干涉条纹图像,通过对干涉条纹图像进行处理得到镜面高度采样,采用泽尼克多项式拟合镜面的曲面函数,测量到了镜面的三维高度数据。干涉条纹图像上相邻条纹与参考面之间的距离相差一个标准光源波长,因而该测量方法的关键是得到条纹波峰或波谷的精确位置,从而达到了镜面相对高度的采样的目的。采用巴特沃斯低通滤波对条纹图像进行滤波,去掉噪声的影响,然后对图像二值化分割出亮条纹,用数学形态法对二值条纹图像细化得到条纹的中心线,结果表明,低通滤波方法能有效地减少细化条纹的分支和断裂。最后定义每条条纹中心线的相对高度,利用前39项泽尼克多项式对镜面高度进行最小二乘法拟合,计算了镜面被测区域的曲面高度数据。该方法可以用来测量强激光引起的镜面热变形。     

Precision measurement of cylinder straightness using a scanning multi-probe system

This paper describes a scanning multi-probe system for measuring straightness profiles of cylinder workpieces. The system consists of two probe-units, each having three displacement probes. The two probe-units, which are placed on the two sides of the test cylinder, are moved by a scanning stage to scan the two opposed straightness profiles of the cylinder simultaneously. A differential output calculated from the probe outputs in each probe-unit cancels the influence of error motions of the scanning stage, and a double integration of the differential output gives the straightness profile. It is verified that the difference between the unknown zero-values of the probes in each probe-unit (zero-difference) will introduce a parabolic error term in the profile evaluation result, which is the largest error source for straightness measurement of long cylinders. To make zero-adjustment accurately, the cylinder is rotated 180° and scanned by the probe-units again after the first scanning. The zero-differences of the probe-units, as well as the straightness profiles of the cylinder, can be accurately evaluated from the output data of the two measurements. The effectiveness of this method is confirmed by theoretical analysis and experimental results. An improved method, which can measure the variation of the zero-difference during the scanning, is also presented.     

Location tracking scanning method based on multi-focus in confocal coordinate measurement system

Confocal microscopy is high precision and widely used method for topography measurement. The surface height information is obtained by peak extraction of the axial response signal (ARS) which axial tomography of the surface is required. Therefore, when scanning large-diameter surfaces with a confocal coordinate measuring system (CCMS), the relative horizontal scanning trajectory (RHST) between the confocal sensor and surface is repeated and time-consuming step motion, which greatly increases the measurement time. To improve the scanning measurement efficiency of CCMS, we propose a new location tracking scanning (LTS) method based on multi-focus. In the LTS method, the RHST is a continuous linear motion during the process of axial tomography, and the horizontal motional surface is located and tracked through a series of focuses to restore the ARS. A generatrix profile of a spherical surface is measured to verify the effectiveness of the proposed method, and the results show that the scanning measurement time can be reduced by more than 90% without loss of accuracy of the profile measurement.     

Evaluating the measurement capability of a wheel profile measurement system by using GR&R

Reliable data with less variation play a key role for acceptance of the usefulness of the measurement output of a wheel profile measurement system (WPMS) in a railway network. However, in practice, most studies are carried out without checking the reliability of data from such a system, which may lead to inappropriate maintenance strategies. To ensure the measurement capability of WPMS and to support robust maintenance in railway systems, this study has evaluated measurement data for the flange height, flange thickness, flange slope, and tread hollowing of rolling stock wheels by using gauge repeatability and reproducibility (GR&R). In this study, acceptance and rejection criteria for the precision-to-tolerance ratio (PTR), signal-to-noise ratio (SNR), and discrimination ratio (DR) have been employed to evaluate the measurement capabilities. For the purpose of illustration, we have implemented a new proposed approach. This approach involves both an analysis using graphs with four regions with a confidence interval (CI) of 95% and an analysis using a graph with three regions with only the predicted values; the latter type of graph represents an innovation made in this study. This graph has the advantages that it can visualize three different levels of data quality in same figure, namely “unacceptable”, “acceptable” and “good”, and also include a number of measures without becoming unclear, which are features that have been missing in previous presentations. The results show that the measurements of the flange slope are on an acceptable level, while those for the flange height, flange thickness and tread hollowing have to be rejected as unacceptable. The action proposed for increasing the quality of data on the flange height, flange thickness and tread hollowing is to enhance the calibration of the WPMS. In conclusion, GR&R is a useful tool to evaluate the measurement capability of WPMS and to provide helpful support for maintenance decision making. This investigation also shows that there is good reason to be careful when selecting measures and when interpreting the results, since, for a certain wheel profile parameter, when one measure is used, the results may be acceptable, but when another measure is used, the results may be unacceptable.     

High accuracy profile measurement of quasi-conical mirror surfaces by laser autocollimation

A method is described for measuring the profile of a quasi-conical mirror surface along one of its axial generators. A laser beam is made to scan the surface and the variation in reflected beam angle is measured by autocollimation. Integrating the angle with respect to distance along the generator gives the profile height to within ±5 nm. The method has application to the metrology of X-ray microscope reflecting objectives     

Pitch deviation measurement of an involute spur gear by a rotary profiling system

This paper presents surface-profiling based gear pitch deviation measurement for an involute spur gear. A rotary profiling system, which consists of an air-bearing spindle and a displacement sensor with a diamond stylus, is employed to measure gear pitch deviation. In measurement of gear pitch deviation, an eccentric error between a gear axis and a motion axis of the rotary stage in the profiling system would affect accuracy of gear profile measurement. In this paper, at first, the influence of the eccentric error on measurement of gear pitch deviation is estimated in computer simulation based on a geometric model of the profiling system. After that, a new scanning method named “opposite-direction dual scanning method” is proposed so that a steep profile of gear flank surface with a local slope of up to 90° can be measured by the developed rotary profiling system. For compensating distortions in the measured gear tooth profile, which are induced not only by the eccentric error but also by a probe offset introduced by the proposed scanning method, a self-calibration and compensation method is applied. To verify the feasibility of the proposed method, measurement of gear pitch deviation of a master involute spur gear with a certificate data is carried out. Measurement uncertainty of the proposed method is also analyzed.     

Development of a dynamic surface shape measurement for magnetic fluid

Traditional measurement techniques such as fringe and stereo projection can hardly measure the black surface shape of magnetic liquid in revolving container which has a cover to prevent the liquid spilling out. To solve this problem, a multi-step measurement method based on linear laser projection is proposed. Modulated laser by synchronous revolving chopper is introduced to obtain the steady projection light curve on the measured location of the magnetic fluid surface. In order to capture the instantaneous reflected light of the projection light curve, a camera used a long exposure time of shooting is used. Taking the advantages of multiple exposure luminance enhancement effect of long exposure time, pictures with high brightness and contrast projection light are obtained. The overall surface shape of the fluid can be reconstructed by many laser projection lines extracted from the pictures captured at different angles of revolving container. A high transparency acrylic cover is adopted to provide good sealing performance and light transmission quality in the experiment. On the base of correction of influence of refractive index of the acrylic cover, the height formula of magnetic fluid surface is derived. The camera installation angle and distance between the camera and the container are not required as the size of container are utilized to calibrate the camera. The relationship between image coordinates and world coordinates is also obtained. According to the height curves of the projection lines and their measuring angles on the container, 3-D surface shape of magnetic fluid is reconstructed. The surface shape is verified indirectly by using the imbalance of the container, and the relative unbalance errors between the measurement results and the results by Shenk dynamic balancing machine under different conditions are between 0.8% and 11%. Another performance experiment on measuring the surface shape of an rubber block indicates that the measurement range of the proposed method is that the slope of the measured surface must be less than 3.94, and the sensitivity is 0.18 mm. All performance of the proposed method is acceptable, so such a complex industrial problem is solved only by a daily digital camera.